OREGON'S experiment with legalized, state-sponsored betting on professional sports is about to be expanded to include basketball. Unless, that is, the National Basketball Association blocks the shot in court with a lawsuit. Earlier this year, Oregon became the only state to sanction point-spread gambling on professional football games as part of its lottery. Proponents in the state legislature ordered the lottery commission to institute that type of gambling as a means of raising money for intercollegiate sports. So far, nearly $2 million out of $5 million in NFL betting here has been turned over to state schools.

That is a lot of money for a small state - especially one without a sales tax - where public and private income from the all-important timber industry is much in question these days. Lottery officials predict another $3.5 million in basketball betting-card sales this season and $19 million overall for intercollegiate athletics and scholarships during the next five years.

But not everyone here views pro sports betting as a windfall. The Portland Oregonian editorialized against ``a sleazy gambling scheme that extracts money from the poor and gullible.'' The newspaper finds the link between gambling and school sports particularly troublesome: ``Is the next step for Oregon college athletes to promote lottery ticket sales?''

Pro sports officials worry that basketball - with fewer players than football, and with a single player's performance perhaps more crucial to the outcome - could be especially susceptible to corruption.

``The history of the college basketball point-shaving scandals of the early 1950s, which have continued until recently at some of the most prestigious universities in the United States, confirms this,'' NBA commissioner David Stern warned the Oregon Lottery Commission recently. ``Missed baskets, unrealized opportunities, and strategic decisions by coaches will come to be viewed as impacting the betting action rather than the contest. ...''

``It's just not a good situation,'' says another NBA official. ``When anyone can walk into a [convenience store], plunk down a dollar, and want us to cover his point spread, it can position our fans against us. With a two-point lead and 20 seconds to go, our fans might boo us.'' This is because under the Oregon system the gambler bets not just on who wins or loses but by how much.

Several other states and the District of Columbia are considering legalized pro sports betting. A proposed ballot initiative in California would include college sports as well.

Those fighting this new form of legal wagering fear that acceptance of lotteries and such things as ``video poker'' (now widespread in Oregon) breaks down societal barriers to gambling, now a $210 billion-a-year industry in the United States.

State lottery officials, who run Oregon's ``Sports Action'' program, say there is no evidence that legal public betting influences the game. But officials did agree to exclude the Portland Trailblazers after the organization and individual players objected. The new basketball betting plan is set to begin next month.